Using SOF as part of the boat design

Discussion in 'Boat Design' started by silentneko, Jan 30, 2014.

  1. upchurchmr
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    upchurchmr Senior Member

    A heat gun is specifically not suggested on aircraft construction. The reason is that if the cloth is heated too high it is permanently damaged and the amount of shrink is reduced. It is almost impossible to tell how hot you have the skin until it starts to melt.

    If you want to do a boat, don't get Ceconite because the aircraft fabric is around 3oz maximum. For a boat you want heavier. I use 8oz for kayaks but would guess you need more for the type of boat you are talking about.

    I get mine from George Dyson (a famous name in SOF boats) at gdyson@gmail.com. George operates a little differently, send him a message requesting information on his stock, he will send it by email. Then send an order (email) he sends you the cloth with an invoice, you send back a check, MO, etc by snail mail (no credit card charging available).
    He has always been very prompt and helpful.

    Another source is kduzucraft.com - there are others that I don't remember.

    Forget using thinned resin, the resin typically goes thru the cloth. (I have not used the 2 part kayak resin which is supposed to be thick.)
    If you want resin on the inside, just paint it on full strength

    I typically use Helmsman Spar Varnish - a one part polyurethane. $40/ gallon. Nice and tough.

    Just realize that the frame is what provides all the strength and stiffness. The skin just keeps the water out. There are those who claim the skin adds a lot of stiffness and strength. I've tested it and it adds "some" but not a lot.

    Cupping in the water is controlled by the distance between the stringers, not the resin.
     
  2. silentneko
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    silentneko Junior Member

    Upchurch, thanks for the info but I think their is some confusion on what I am actually going to do. SOF anything is pointless around here cause we scrape oysters, so a SOF boat wouldn't last but a few trips. I am not building a SOF power boat, I am using SOF to achieve the shapes I want. Then I will add several layers of thicker glass, fair it all out, and create a mold with it. The actual skiffs will be built out of the mold with hand laid biaxials and such.

    I will get an iron, but I will probably use it in combo with the heat gun to get the results I want. As long as I work slow and am careful I should be able to keep the cloth from getting damaged. At 9-12 buck a yard for 72" wide ceconite I can afford a few mistakes and trials.

    Thanks for the material sources, I'll look into it, but I don't do anything anymore without a credit card unless it is in person, been burned to many times and the credit has built in protection.
     
  3. upchurchmr
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    upchurchmr Senior Member

    I must have missed your method for the build.
    There is no benefit to mixing iron and heat gun.
    Since you are not going to depend upon the dacron skin for the final shape, I would be happy using the heat gun.
    Just don't let the heat gun stop, the cloth heats up really fast if you stop.

    To each his own on the payment. Any time you use a credit card someone can use it twice, we were burned using it locally. Not so with a check. I've dealt with Dyson 7 times with no issue, but he does not have the very light cloth. However, his heavier cloth is cheaper than the Ceconite.
     
  4. silentneko
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    silentneko Junior Member

    I know it's been a while, but I am actually moving forward with the design phase of my plan. I bought some of the 1.87oz uncertified ceconite and it is some pretty cool stuff. It shrinks great with the heat gun and is making the exact shapes I envisioned.

    However, it is not drum tight. I made a 1/12th scale test model and it is fairly tight and holds it's shape well, but I am concerned it would sag on a larger scale. Will the 3oz or higher ceconites be more rigid when heated and shrunk then the 1.87oz?

    I'm testing laminations and not sure which way I will go just yet, but if I get a shape I like I will post up a pick or 2.
     
  5. silentneko
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    silentneko Junior Member

    Here was my test 1/12th model. It is very far from the final design I envisioned, but I had some scrap OSB, a hot glue gun, and 30 minutes to spare, so here we are.

    [​IMG]

    [​IMG]

    [​IMG]
     
  6. silentneko
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    silentneko Junior Member

    I'm back to thinking about moving forward on this project. I now have 2 boats I wish to build over the next few years. One is a small 12-13ft skiff to be used for flats fishing and exploring rivers, and the next will be my main boat, a 16-17ft panga style.

    I'm considering the wisdom of the guys here and I will be using the frame and skin as a positive mold. I contacted the company that makes Ceconite and they advised it could be used how I want, but those that do use it for molding use it like peel ply, not as part of the lamination. This actually might make things easier.

    Does anyone have a link to some panga designs in the 16-17ft range? Any advise on this type of design?
     
  7. Squidly-Diddly
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    Squidly-Diddly Senior Member

    fiber-glass over skin worked fine for me.

    I built a pvc tube skin on frame kayak with thin waterproof nylon fabric, duct-tapped to the gunnel tube all the way around. (if I was gonna do it again I'd probably wrap little strips of something and screw the strips to the gunnel)

    But when I put it in water the fabric bowed in a bit too much and I was nearly decks awash, so next I just put a single layer of fiber-glass and resin and it seemed about perfect.

    IIRC the biggest spans between stringers was less than 7".

    Later, when I was junking it I tested to see how the two layers would act when attacked with sharp objects, and it seemed like they pretty much worked together just fine, or at least didn't work against each other.
     
  8. Skyak
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    Skyak Senior Member

    I have a 14ft 28lb kayak from Polk boats and it used a very thin proprietary flexible layup. From the looks and what I have read it is two layers of fiberglass and one layer of high strength nylon. The point is that it is possible to make extremely light and durable boats with thin epoxy glass faric layup, and the fabric can be part of the layup without delamination over long life.

    silentneko,
    From what I can see, you want to make small tough flatbottom outboard boats. The only thing the skin step offers is a complex hollow in the bow, and the cost will be a thick layup to handle pounding. I suspect that fiberglass over marine ply would offer a cheaper tougher and lighter boat.
     
  9. silentneko
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    silentneko Junior Member

    I think if I go through with this plan I would build the frame, stretch and shrink the material, Use silicone to radius the seams and laps, and then spray it all down with PVA release. I'm sure it is possible to use the ceconite as part of the layup, but being I'll be attaching the stringers and such on the inside it makes me nervous. I'd rather just use it all as a positive mold.
    I'm looking to make a panga, and while it is possible to make one out of ply and glass, it will take a lot of trial and error to get the sharp curves I'm looking for. With the SOF setup I want to do I can have the basic design framing done within a few days once I start. I only have worked with epoxy so I'll probably keep with that. With the stringer system and bulkhead design, plus the foam filling, I think I'll be able to turn out a decently light hull even with solid glass.
    Here are the pangas I want, but need them to come shorter.
    http://www.pangamarine.com/
     
  10. silentneko
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    silentneko Junior Member

    So yet again I am back to thinking about this. I had to put everything on hold while I went back to school, but now free time and money are coming back into play.

    The plan has changed, instead of a full sized boat I am going to build a small skiff, that will fold in the middle. this way it will fit in the back of my tacoma. I'll power it with a 2.5-5hp motor. I'll start designing it in a month or so when things really quiet down a bit.
     
  11. CDBarry
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    CDBarry Senior Member

    One possible issue is that when you sand the plug to get the added FRP layers smooth, the part that is better supported will sand more readily whereas the material spanning supports will not be sanded as well, and you will form a slight crease or trough there, that might look odd.
     
  12. silentneko
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    silentneko Junior Member

    Good point, I assume you mean the positive mold I'll be using, the plug itself won't be sanded until it's been removed. At that point the layup should be strong enough for sanding.
     
  13. PAR
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    PAR Yacht Designer/Builder

    This seems to be a really difficult way to make a plug or mold, unless you can make the skin uniformly rigid, so any subsequent fairing operations can take place on a stable surface.
     
  14. silentneko
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    silentneko Junior Member

    It will either be a total hassle, or completely brilliant! Nothing ventured, nothing gained right, lol. I often have off beat ideas, but this one I think is very doable, my small scale tests came out well. I'm gonna do a 1/4 scale trial to see any issues that might come up.
     

  15. SamSam
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    SamSam Senior Member

    This is confusing. You use a plug to make a mold and a mold to make a piece. What you're describing is using a positive mold to make a boat/piece, not to make a plug.

    The boat/piece will require sanding and grinding inside to attach structure, (any silicone residue/contamination will make any subsequent fiberglass work difficult or even impossible) and a tremendous amount of sanding and fairing on the outside to make a finished boat. Depending on what you want it to look like. Lumpy and bumpy will be easy, if you like the look of a polished turd. If you want the outside finish to even be close to a mediocre mass manufactured boat, you're looking at the above, a tremendous etc, etc.

    Normally a boat is made inside a sturdy mold with a mirror like finish, so when the boat is pulled from the mold, there will be no work required to the outside. It's already shiny and smooth, ready to go and it even has the waterproof gelcoat on it.

    While the hull is still in the mold, all the supporting structure is installed, usually you can get right in the mold to do the work. After that is installed, the hull is pulled from the mold and it retains it's intended shape.

    Using a positive mold such as you plan, you'll have to pull the piece off to install any structure, and since it has no structure it will be weak and floppy, flat surfaces will tend to bow or cup, things will twist, etc. which will be locked in by the structure you glass into place. You can't get in it to work, as it is too weak and floppy. The structure itself, as the glass tabbing sets and slightly shrinks, will probably introduce more defects.

    After the structure is in, then you can flop it over and spend as much or as little time as you want on fairing and filling and fairing and filling and eventually get it to where it's time to paint it for waterproofing or UV protection.

    Maybe I misunderstood your plan for making this boat...?
     
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